La aplicación del modelo simulativo de f. Newhall (1976) a series de datos climáticos, del área meridional de Lleida, produce la aparición generalizada del régimen de humedad USTIC. Tal resultado es incoherente con las características de los suelos del clima de esta comarca y ha motivado la elaboración de un nuevo modelo simulativo del régimen de humedad de los suelos, cuyas características principales son: - considerar varios tipos de perfil de suelo. - posibilidad de utilizar datos de precipitación diaria o mensual. - tiene en cuenta la infiltración real del agua de lluvia. - tiene en cuenta las características de los suelos para modelizar los procesos de infiltración y evapotranspiración. - coinciden muy satisfactoriamente los resultados experimentales con los obtenidos mediante el modelo. El modelo simulativo propuesto da como resultado que el regimen de humedad de los suelos del área meridional de Lleida es XEREIC-I y ARIDIC en los de menos capacidad de retención de agua. / Lack of irrigation water in southern Lleida (north-east of Spain) restricts the possibilities of an intensive use of soils. To better this situation we need a good information about soil moisture contents, Esther in the present situation or in a future implantation of some irrigation methods.The present research has been developed from 1984 to 1988. Its first aim has been to study the soil moisture contents in the above mentioned area during these years . The soil moisture contents has been determined in order to establish the real situation of the moisture control section; from twenty-two initial control points we selected two representative ones.The second aim has been to determine the moisture regimes of soils in the above mentioned area in order to determine its classification as Soil Taxonomy (USDA 1975) is concerned, to avoid the problems that arose from the fact of not knowing whether the regime was Aridic or not.In this research, Franklin Newhall's simulation model (1976) has been proved inadequate when applied in a semiarid zone like the studied. Therefore we propose a new simulation model for the soil moisture regimes with the following main properties: (1) possibility of using daily or monthly precipitation data; (2) possibility of taking account the efficiency of infiltration of rainfall water: (3) possibility of using the model soil profiles of different available water capacity; (4) it takes into account local soils and local whether properties; (5) it allows knowing the state of the moisture control section each day during each year of the studied series (7) it is very easy to use in a Personal Computer with MS-DOS operating system.Finally, there is a great coincidence between the experimental mentioned results and the estimation obtained by applying the model proponed in this work. Therefore, the soil moisture regimes in southern Lleida are Xeric and Aridic in soils with lower available water capacity, opposite to Ustic regime obtained by applying the F. Newhall's model.